Tommy Rettig as Jeff Miller with Donald Keeler as Porky in Lassie (1956).

Rettig later told interviewers that he longed for a life as a normal teenager, and after four seasons he was able to get out of his contract. He was also critical of the treatment and compensation of child actors of his day. He reportedly received no residual payments from his work in the Lassie series, even though it was syndicated and widely shown under the title Jeff's Collie.

From 1964 to 1965, he co-starred with another former child actor, Tony Dow, in the ABC television soap opera for teens Never Too Young.[5] With the group "The TR-4", he recorded the song by that title on the Velvet Tone label.[6] While he was the TR-4 group's co-manager, he did not sing with them. Rettig only co-wrote the song in hopes of the TV soap using it as their theme. It was not chosen.[7] He was cast as Frank in the 1965 "The Firebrand" of the NBC education drama series Mr. Novak, starring James Franciscus.

As an adult, Rettig preferred to be called "Tom." He found the transition from child star difficult, and had several well-publicized legal entanglements relating to illegal recreational drugs (a conviction for growing marijuana on his farm, and a cocaine possession charge of which he was exonerated). Some years after he left acting, he became a motivational speaker, which—through work on computer mailing lists—led to involvement in the early days of personal computers.

Rettig made a guest appearance in an episode of the later television series The New Lassie, with Jon Provost, which aired on October 25, 1991. The series featured appearances from two other Lassie veterans, Roddy McDowall, who had starred in the first movie Lassie Come Home (1943) and June Lockhart, who had starred in the 1945 movie Son of Lassie, and the television series (as Timmy's mother in the years after Rettig left the show).